Air Flow Cuts Off July 19, 2016, 10:40:20 pm The air flow from both Vent and AC completely cuts out and then comes back. I think this maybe due to a drop in vacuum pressure when accelerating or going up grades. Before I place my wallet at the throne of a service writer, anyone here have any ideas about this? Testing/Inspecting vacuum lines is way over my pay grade.
Re: Air Flow Cuts Off Reply #1 – July 19, 2016, 11:49:57 pm Did this problem start at the same time as when the engine was possessed? Larry
Re: Air Flow Cuts Off Reply #2 – July 20, 2016, 10:59:47 am We noticed this several months back, Larry. It gets noticed more when it's hot.
Re: Air Flow Cuts Off Reply #3 – July 20, 2016, 05:41:07 pm The HVAC system's controls operate off stored engine vacuum. During times when the throttle is open widely, next to no vacuum is present. To maintain a constant vacuum source for the HVAC, a vacuum storage container is provided.When the engine vacuum is low, as when going up a grade, the low vacuum is isolated by a check valve, located between the intake manifold and the vacuum storage container. This maintains vacuum to the HVAC system, when no engine vacuum is present..Your symptoms could be caused by a defective check valve.Might even have something to do with the engine problem.Larry 2 Likes
Re: Air Flow Cuts Off Reply #4 – July 21, 2016, 02:07:19 pm I noticed something awry with LDy Lulubelle's vent/AC/upper heat fairly early on, but thought it was my learning curve. Then learned, after the many discussions about vacuum/load/etc., that it was her--not me--that had the problem...but also read several folks talk herenabout how expensive it was to address (removing the doghouse/dash/etc., so I just lived with it. I happened to mention it to Jake (the service manager at the Merle Kelly Ford dealership in Chanute, KS I recently mentioned in another post), thinking he could give me a better idea of cost, because it was beastly hot & I didn't relish sailing across KS to Denver with the cold air blowing up on the windshield through the defroster vent whenever the engine was under any load at all--as in anything other than park/neutral/going downhill... He pulled the fabric dash cover off (the one held on by velcro strips) & found an access panel in the middle of the dash, which he said popped off easily with a screwdriver; inside he found that a critter had made a home there sometime & chewed into the vacuum hoses to the vent/AC/upper heat. He said there was fortunately enough slack in the hose that they just cut off the chewed end & reattached...presto-chango I have air blowing quite nicely on me all the time, except when she's really chugging up a grade. I didn't even know there was anything but a vinyl dash under that fabric cover. Always something new to learn. Good luck with yours.
Re: Air Flow Cuts Off Reply #5 – July 21, 2016, 02:41:08 pm Excellent info for my maintenance book, thanks againBob
Re: Air Flow Cuts Off Reply #6 – July 25, 2016, 11:48:12 pm This is a common problem with E450 RVs or whatever else might be built on the chassis discussed a bit on this form or the previous Yahoo version which I'm not sure is accessible from here, maybe it is but more extensively on other online forums etc. There is supposed to be a vacuum reservoir which is buried very deep under the battery over the passenger front wheel well and so very labor-intensive to replace. The workaround which worked for me is bypass the vacuum reservoir, this had already been done by someone else so that's the part I don't know how to access. I already had a tube going through the firewall in the passenger front foot well area with no T going to any vacuum reservoir. I added about 6 feet of tubing ( this acts as a volume to replace the vacuum reservoir) and the check valve which was completely missing and basically strapped it to my battery. I was going to live with the problem until I started having other error codes that seem vacuum related potentially. Those were apparently caused by a bad gasket on the K&N air filter the previous owner installed. K&N and gave me a new gasket but I haven't put it on. yet I'm just going with the Ford dealer paper one until I figure it gets old